This invention relates to a process for reading-out information from a layered residually or remanent electrically polarized data carrier, corresponding to the recorded information in local domains by scanning the polarized domains by means of electron beams.
A substantial target of development in the area of data processing are information memories with high data capacity. Stationary electrically erasable memories on a silicon base with memory capacities of 10.sup.6 bit/cm.sup.2 and movable magnetically erasable memories (such as a band, plate, or drum) of 10.sup.7 bit/cm.sup.2 are presently commercially in use. However, memories with substantially higher storage capacities than 10.sup.8 bit/cm.sup.2 are desired and in great demand.
In addition to the conventional, widespread semi-conductor memories and magnetic memories, different processes, based on other physical principles, for recording and selecting information from data memories have already been examined and described. Thus, with multi-dimensional storage by means of laser holography or by means of photochemical hole-burning, the information is entered into the storage medium by a laser beam. Reading-out also takes place by a laser beam. A further direction of development is concerned with the use of electron beams for reading in and reading out. The electron beam has the advantage compared with the laser of a substantially lower beam diameter. A higher local dispersion and thus a higher storage capacity is thereby achieved. With this method, a non-erasable and read only memory has been recently produced by burning minute holes in aluminum foil.
As an analogy to the magnetic memory which is based on the magnetization of ferromagnetic domains, electrically polarizable media are already examined early on for suitability as solid-state memories. In U.S. Pat. No. 2,698,928, several basic processes for reading in and reading out information in or from residually electrically polarizable data carriers are described. The reading-in or writing takes place on a residually electrically polarizable data carrier which is provided with an electrically conductive base layer which is passed by an electrode which is charged with an electric potential corresponding to the information to be recorded. Alternatively, the information can also be entered into the polarizable medium by means of electron beams. An electron beam can also be used according to U.S. Pat. No. 2,698,928 for reading-out. Such a high field strength is produced in the polarized medium by the electron beam, that the polarized domains are reversed in polarity. During the reversing of the polarity, electric potentials are produced across electrodes, which potentials are detected as a read-out signal. In addition, the polarized data carrier can be charged with ultrasonic waves. The piezoelectric signal stored on the data carrier is then modulated with the ultrasonic frequency of the waves. In this case, the signal-to-noise ratio can be improved by frequency selective amplifiers.
This method of reading-out suffers from the disadvantage that the original polarization state and thus also the recorded information is erased by the relatively high field strength arising from the electron beam. Furthermore, the sensitivity leaves a lot to be desired; that is, it is difficult to achieve a sufficiently high signal-to-noise ratio.
A read-out process based on the principle of electron beam expansion is described in U.S. Pat. No. 4,059,827. The data carrier here is a ferroelectric polyvinylidene fluoride film. The read-out signal is produced by the metallized back layer of the data carrier being maintained at such a high negative potential, that the electron beam is diverted onto a grid-shaped collector electrode. If the data carrier is now electrically polarized corresponding to the recorded information, then the deflected beam is moved to the side or expanded, depending on the extent of the polarization charges. The information recorded in the form of a residual electric polarization can then be recovered again on the collector electrode in the form of an electric potential. This process suffers from the disadvantage that the data carrier must remain under high vacuum after entering the information and until read-out, since in air, a compensation of the polarization charges takes place immediately and thus the read-out is rendered more difficult or even impossible. Moreover, the strength of the read-out signal is greatly dependent on the geometry of the electrode, such that the spacial arrangement of the electrodes and the electron beam guns is very critical. This demands high precision when guiding the data carrier and in the arrangement of the read-out head. For these reasons, a high susceptance to disturbance is to be expected, especially when the process is optimized with respect to high sensitivity and high lateral resolution.